(a) Field of the Invention
This invention relates to diagnostic radiology and in particular relates to the use of high energy radiation to form images of internal structures upon a sensing means such as x-ray film. The invention more particularly relates to a method and apparatus for reducing detection of radiation scatter in forming such images.
(b) History of the Prior Art
Originally, x-ray photographs were taken simply by directing x-rays from a source, e.g., an original rontgen ray tube, through an object such as an anatomical structure to a detector such as an x-ray film. This historical arrangement did not include additional devices to reduce hazards to a patient or to enhance the quality of the detected x-ray image.
Later x-ray devices not only provided improved x-ray tubes such as tubes which could independently control intensity and wave length of x-rays but also incorporated filters for eliminating radiation outside of the useful x-ray range and included means for enhancing the contrast of the image by eliminating at least a portion of radiation scatter from the object such as a patient to the detector. Such scatter often results when high energy radiation interacts with molecular fields or particles. Scattered radiation is usually emitted in a direction different than the direction of the incoming primary radiation. The scattered radiation thus causes exposure of the detector to radiation at all locations thus reducing contrast of the detected image with the background.
The most usual method for reducing scatter historically has been and remains radiographic grids which consist of a series of lead foil strips separated by x-ray partially transparent spacers. The lead foil acts to intercept secondary or scattered radiation which approaches the detector at an inappropriate angle. Such grids have, however, certain undesirable characteristics. For example, contrast is still not as high as desired since all scatter is still not eliminated, primaries are absorbed by interspaces and grid lines become apparent on the x-ray image since the lead strips absorb primary radiation from the radiation source.
Attempts have been made to eliminate the appearance of the grid pattern in the x-ray image by moving the grid in a direction essentially perpendicular to radiation passing from the source to the detector; however, such a moving grid did nothing to increase contrast. There has also been an attempt to utilize linearly moving aligned slit devices to increase contrast. The devices have to be moved at a uniform speed and have to reach that speed before the x-ray is taken. This requires that the x-ray be taken in a precisely timed relationship to slit motion. Furthermore, vibration within the system cannot be tolerated and absolutely uniform x-ray output must be maintained during exposure to prevent unwanted patterns on the detector. Currently and perhaps subsequent to the present invention, an attempt is being made to increase contrast by mounting two slitted discs on a single axis and rotating the discs about the single axis while directing x-rays from the axis through the first slitted disc to the object or patient through the second slitted disc and a grid to the detector. This device has not proven desirable since a patient or object and detector, in order to be placed in a perpendicular relationship to incoming radiation, must of necessity be at an angle to the rotating discs. Such arrangement permits very little flexibility with respect to the location of the patient in relationship to the x-ray source and the rotating discs and contrast is not as good as is desirable. Furthermore, due to the use of the grid, grid lines are still present.